Various type chemical processes are commonly carried out in large, stirred vessels which are frequently provided with auxiliary equipment, such as baffles, heat transfer coils which enable heat to be supplied or extracted from the contents of the vessels, and the like. In many cases, however, such processes eventually produce undesirable deposits on the surfaces of the equipment with which the reaction mixtures come into contact. Such deposits interfere with the efficient transfer of heat to and from the interior of the vessels. Further, these deposits have a tendency to deteriorate and to partially fragment resulting in contamination of the reaction mixture and the products produced therefrom. This problem is particularly prevalent in polymerization type reactions, since the deposits, or "build-up", of solid polymer on reactor surfaces, not only interferes with heat transfer, but decreases productivity and adversely affects polymer quality.
This problem is particularly bad in the commercial production of polymers and copolymers of vinyl and vinylidene halides, when polymerized alone or with other vinylidene monomers having a terminal CH.sub.2 .dbd.C&lt; group, or with polymerizable monoolefinic monomers. For example, in the commercial production of vinyl chloride polymers, the same are usually produced in the form of discrete particles by polymerization in aqueous suspension systems. When employing such a polymerization system, the vinyl chloride, and other comonomers when used, are maintained in the form of small discrete droplets by the use of suspending agents and agitation. When the reaction is complete, the resultant polymer is washed and dried. These aqueous suspension systems polymerization reactions are usually conducted under pressure in metal reactors equipped with baffles and high speed agitators. However, these suspension systems are inherently unstable and during the polymerization reaction, vinyl chloride polymer builds up on the interior surfaces of the polymerization reactor, including the surfaces of the baffles and agitator. Obviously, this polymer buildup must be removed since it results in further formation of polymer buildup which in turn results in a crust that adversely affects heat transfer and contaminates the polymer being produced.
The nature of the polymer buildup, or insoluble deposit on the walls of the reactor, is such that in the commercial production of polymers, as described above, it has in the past been standard practice, after each polymerization reaction is completed, to have an operator enter the reactor and scrape the polymer buildup off the walls and off the baffles and agitator. An operation such as this is not only costly, both in labor and down-time of the reactor, but presents potential health hazards as well. While various methods have heretofore been proposed to reduce the amount and nature of polymer buildup on polymerization reactor surfaces, such as solvent cleaning, various hydraulic and mechanical reactor cleaners, and the like, none has proved to be the ultimate in polymer buildup removal. That is to say, these various methods and apparatus have done an acceptable job, but there is still room for improvement in this area, particularly, from an economic point of view.
In copending application for U.S. patent, Ser. No. 574,037, filed May 2, 1975, in the names of Donald E. Witenhafer, James B. Haehn and Louis Cohen, there is disclosed and claimed a process for coating the inner surfaces of a polymerization vessel or reactor with an aqueous alkali metal hydroxide coating solution containing a straight chain or branched polyaromatic amine. This claimed process has proved to be more than satisfactory in achieving the intended results and multiple reactions can be run in the polymerization vessel so coated without opening the same between each reaction. However, experience with such process, on a commercial scale, has shown that more dilute coating solutions would be desirable in order to reduce costs and more importantly, to reduce the color of said solutions. Since the polyaromatic amines are colored condensation polymers, there is a tendency, on occasion, for some of the polymer particles being formed during the polymerization reaction in the presence of the coating on the inner surfaces of the polymerizer to become discolored which, of course, is undesirable and to be avoided, if possible. It should be pointed out, however, that the effectiveness of such coating solutions in reducing, and substantially eliminating, polymer buildup is not affected by such discoloration problem. Therefore, it would be desirable to have an improved coating solution which substantially eliminates the potential discoloration problem.